Relationship between radioactivity and toxicity in some medicinal plants

Plants absorb water, nutrients and minerals from the soil through their root. Also, minerals, the radionuclides present in the growing media also are absorbed by plant parts following the same pathway. Consequently, it is important to determine the concentrations of these radionuclides in edible plants to access the associated risk to human health. In the present work, the levels of natural radioactivity and the level of some toxic elements in 17 medicinal plants, commonly used in Egypt, were measured using high-purity germanium gamma spectrometry and atomic absorption, respectively. The investigated plants were sub-grouped according to the edible parts into leave samples (n = 8), roots (n = 3), and seeds (n = 6). Also, the specific activity of both radon and thoron was measured by using alpha emitters registration which is emitted from radon and thoron gases in CR-39 nuclear track detectors. Additionally, the concentration of some toxic elements (Cu, Zn, Cd and, Pb) in six samples of medicinal plants was determined by atomic absorption spectrometry.

Ra point source. The relative efficiency curve was normalized for the 250 ml capacity beakers by the concentration of chemically pure potassium chloride solution in distilled water. Similar sample size was used to obtain the absolute efficiency curve. The detector was surrounded with lead shielding to reduce the interference with background radiation. The activity concentrations were calculated as follows: (a) 238 U concentrations were determined by measuring the 295.1 (19.2%), 352 (37.2%) keV γ-rays from 214 Pb, the 609.3 (46.1%) and 1120.3(15.1%) keV γ-rays from 214 Bi. (b) 232 Th activity was determined from the γ-peaks of 238.6 (43.6%) keV from 212 Pb, 911.2 (29.0%) and 969.0 (23.2%) keV from 228 Ac, and 583.0 (31.0%) keV γ-rays from 208 Tl. (c) 40 K concentration was measured from its 1460 (10.7%) keV γ-line. (d) 226 Ra concentration was determined by measuring the γ peak of 186 (3.3%).
Calculations of count rates for each detected radionuclide depend on the establishment of secular equilibrium reached between 238 U, and 232 Th and for their decay products. Radioactivity concentrations of each sample were measured for about 48 h 16 . Radon measurement. Polyallyl Diglyol Carbonate (CR-39) nuclear track detector of 500 μm thickness with the chemical composition of (C 12 H 18 O 7 ) and density of 1.31 g cm −1 was used in this work. A nuclear track detector has a high sensitivity to record the tracks of alpha particles, proton, and fission fragments because it has the bonds of weak carbon that break when exposed to ionizing radiation. The advantage of a nuclear track detector is the technology does not require sophisticated electrical equipment and is used for determining the radioactive substance due to their availability and accuracy 17 . A weighed amount of each sample was placed in plastic containers with dimensions 8.5 cm in height and 4 cm in average diameter. A piece of CR-39 detector of area 1 × 1 cm 2 was embedded in the sample. At the same, time a second piece of the CR-39 detector was held at the top of the container (Fig. 1). The containers were left at room temperature for three months of exposure time. During this period alpha particles from the decay of radon, thoron, and their daughters bombard the CR-39 nuclear track detectors in the containers 18 . After, exposure the detectors were chemically etched in a 6.25N NaOH at 70 °C for 6 h to reveal the tracks, which were counted using an optical microscope. This experimental setup ensured that the detector in the bulk sample recorded alpha particles from radon, thoron, and their daughter products present in the investigated samples. The upper detector, however, only recorded the 222 Rn component. Consequently, the difference in the track densities between the two detectors represents the content of 220 Rn and daughters in the sample. The density of tracks counted was assumed proportional to the 220,222 Rn exposure. The specific activity of radon in the investigated samples was calculated by using the following formula 19 where the variables: ρ Rn is the radon track density (track cm −2 ), "η" is the efficiency factor for the CR-39 track detector this factor depended on the detector efficiency for the detection of alpha particles emitted from radon and its progeny 20 and, "t" is the exposure time (90 days).
Atomic absorption measurements. The levels of four toxic elements including Cupper (Cu), Zink (Zn), Cadmium (Cd), and lead (Pb) contained in six medicinal plant samples were estimated. In this study were analyzed using Atomic absorption spectrometry (AAS) which is widely used for the determination of trace elements in all kinds of samples. In Atomic absorption spectrometry, a beam of light passes the sample. Depending on the concentration of the element, a certain amount of light is absorbed. The concentration of the element can be estimated by comparing the intensity of the initial beam with the beam after passing the sample. The AAS instruments contain separate light sources for each element since each element absorbs light of a certain wavelength. AAS is often a technique for determining just one element per analysis.

Statistical analysis.
The results were statistically analyzed using the SPSS 10.0 software package (SPSS, Chicago, IL, USA) in accordance with accepted statistical practices. All measurements were performed in triplicates, where the average values (± standard deviation) were computed. (1)

Results
Analysis of gamma spectrometry. www.nature.com/scientificreports/ and P14 which are belong to root and seed categories respectively. While 232 Th was recorded as the lowest value (3.96 ± 0.9 Bqkg −1 ) in P7 (Pimpinella anisum) which belong to the root category. Also, the results showed that all radionuclides had high contribution in leaves samples than roots and seeds (Fig. 3).
Assessment of radiological hazards. The radiological effects of radionuclides caused by internal and exterior alpha radiation can be evaluated using outdoor and indoor absorbed gamma dose rate (Dout and Din), outdoor and indoor annual effective doses (AEDE out and AEDE in ), radium equivalent activity (Raeq), internal hazard index (Hin), and outdoor and indoor excess lifetime cancer risk (ELCR out , ELCR in ). In all calculations, A Ra , A Th and, A K are the activity concentrations of 226 Ra, 232 Th and, 40 K in Bqkg −1 .

Radium equivalent activity (Ra eq ).
The exposure to radiation has been defined in terms of radium equivalent activity (in Bqkg −1 ) and defined as the sum of the activity of 238 U, 232 Th, and 40 K based on the assumption that 10 Bqkg −1 of 238 U, 7 Bqkg −1 of 232 Th, and 130 Bqkg −1 of 40 K produced the same γ-ray dose rates and it used to compare the specific activity of materials containing different amounts of 226 Ra, 232 Th and, 40 K in a single value 20 .
The mean values of radium equivalent (Ra eq ) in seed, root and leave samples were147. 15    www.nature.com/scientificreports/

Outdoor and indoor annual effective dose rates (AEDE
Din (nGh-1) www.nature.com/scientificreports/ People typically spend 80% of their time outside, whereas the remaining 20% of the time is spent inside their homes. Accordingly, the interior and outdoor occupancy variables were set to 0.8 and 0.2, respectively. AEDE out and AEDE in were estimated using the following equation 10,23 : Also both AEDE out and AEDE in recorded their highest mean values (0.144 ± 0.002 and 1.153 ± 0.02 mSvy −1 respectively) in leave samples which were higher than the worldwide average values (0.07 mSvy −1 for outdoor and 0.410 mSvy −1 for indoor) (Fig. 6) 24 .

Internal hazard index (H in ).
In addition to exposure to radioactivity from the outside, radon and its shortlived byproducts are known to be harmful to human health, particularly the respiratory system 25 . The internal hazard index (H in ) 26 was used to measure the interior exposure to radon and its daughter products. For safe boundaries, the internal hazard index should be less than unity. In seed samples, roots, and leaves, the average readings of H in were 0.538 ± 0.002, 0.570 ± 0.003, and 0.935 ± 0.01, respectively. As a result, the computed average values of the H in index were below one. 27 has specified the gamma activity concentration index, I γ , as another measure of radiation hazard which defined as the risk arising from gamma radiation associated with radioactive natural nuclei in the investigated samples and calculated from equation depending on activity concentrations of 226 Ra, 232 Th and 40 K. Its formula is as follows:

Gamma index (I γ ). The European Commission
Because of the excessive external gamma radiation generated by natural radionuclides in the screened samples, the gamma index I γ has a positive correlation with the yearly dose rate. In the current study, where the safety value for this index is 1, it was found that the maximum value was 1.86 ± 0.06 in leave samples. www.nature.com/scientificreports/ Outdoor and indoor excess lifetime cancer risk (ELCRout & ELCRin). The following formulae were utilized to access the potential for outdoor and indoor cancer risk due to radiation exposure, while accounting for the average human age of 70 years 24,28 : Also, the highest average values of outdoor and indoor excess lifetime cancer risk in leave samples were (0.47 ± 0.008 and 3.80 ± 0.07 respectively). Which are higher than the recommended levels of 0.29 × 10 -3 .

Toxic element results.
There are four toxic elements Cu, Zn, Cd and, Pb were determined in six medicinal plant samples (P2, P3, P7, P9, P11 and, P17) by flame atomic absorption spectrometry. Results show that Zink recorded the highest concentration in P7 (Ginger) 22.96 mg kg −1 and lead recorded the highest concentration in P2 (Thyme) at 15.80 mg kg −1 . While the concentration of Cu ranged from 2.50 to 9.67 mg kg −1 and Cd from 1.21 to 1.65 mg kg −1 ( Table 3). Both Zink and lead demonstrated the highest contribution among the investigated samples (Fig. 7). The relation between radon concentrations and four toxic elements was demonstrated in Fig. 8.

Discussion
The average values of 226 Ra in the examined medicinal plants are slightly higher than the recommended threshold of 33 Bqkg −1 , but the average values of 238 U in leaf samples are slightly higher than the typical world average value of 32 Bqkg −1 . At the same, time 222 Rn concentrations are much higher than the lower recommended level of ICRP (100-300 Bqm −3 ) 29 . While 40 K is much higher than the reference value 412 Bqkg −130 . The high concentrations of 40 K (892 ± 17,1190 ± 22, and 1416 ± 27 Bqkg −1 ) in seeds, roots, and leaves respectively may be due to unreasonable applications of potassium-containing fertilizer in soil from which medicinal plants absorb potassium in different amounts according to their metabolism. Also, the high concentrations of 40 K are very significant because potassium is taken in through food and is completely absorbed upon ingestion, moving quickly from the gastrointestinal tract to the bloodstream. The variation in the activity concentrations of the different medicinal plants may be due to the fact that some of these plants tend to absorb more of certain elements than other plants. The activity concentration of a plant is also related to the soil, pH, and more generally the geographic region, in which the plant grows 31 . The highest concentrations of all radionuclides were found in P9 (Tilia Europea) from the leaves category, P11 (Syzygium aromaticum) from the seeds category and, P17 (Alpinia officinarum) from the roots category which is widely used for treating menstrual disorders as well as many other diseases. The mean activity concentration of 238 U, 232 Th and, 40 K in the present work are compared with other works 11,[32][33][34][35] and are demonstrated in Fig. 9. This comparison show that the present study agrees with those measured in other reported countries, however the mean activity concentration of 238 U in the present work are higher than those reported in Serbia 32 , Nigeria 33 , Italy 34 , and Brazil 35 but is little less than those reported in Gana 11 . Also, 232 Th in the present work is higher than reported countries except for Gana but 40 K in the present work is significantly higher than reported countries.
From the present, study we found that some of the hazard indices are higher than the recommended level 36 such as gamma index (I γ ), outdoor and indoor excess lifetime cancer risk (ELCRout & ELCRin) however the workers in medicinal plants stores are externally exposed to radiation due to natural radionuclides present in these plants. Besides radioactivity toxic elements were determined in the investigated samples where both Zink and lead recorded high concentrations in the studied samples. The abnormal accumulation of these toxic elements in the human body is associated with health risks. Zink intoxication for example causes heart disease, night blindness, nausea, stomach pain, and diarrhea 37 . At the same time lead is known to cause bone marrow and kidney damage 38 . In, contrast Cu and Cd concentrations recorded lower levels in studied samples. A similar study 38 determine trace elements (Cu, Fe, Zn, Mn, Cr, Ni, Pb, Se, As, and Cd) in Chinese herbal drugs. The authors found that the high concentration of Pb (0-6.59 μg g −1 ) and Zn (4.61-20.27 μg g −1 ) While Cupper (2.64-12.7 μg g −1 ) and Cadmium were not detected in the investigated samples. Also, similar study conducted  www.nature.com/scientificreports/ natural products (like phytocompounds) due to their substantial antiviral activity against SARS-CoV-2 and other coronaviruses 41 .

Conclusions
Some medicinal plants daily used in Egypt were studied and the activity concentration of the naturally occurring radionuclides in medicinal plant samples was determined using hyper-pure germanium detectors and solid-state nuclear track detectors. The activity concentrations of naturally occurring radionuclides are higher than the average worldwide ranges in all leave samples. 40 K recorded significantly higher concentrations in all samples. Also, all radiological parameters are higher in leave samples than the recommended allowable limit. Zn and Pb have the highest concentrations in all six samples under investigation. So Percussions must be taken into consideration for workers in these plant stores. Additionally, the data presented in this study will be used as a baseline to gauge how much radiation and toxic elements residents have been exposed to. The study revealed that there are no relations were found between radon concentrations and toxic elements in some investigated samples.